You will very likely find several answers to the "best security application in it's own category", since different users have different needs and preferences. There is, however, certain consensus about it, you can search on Google for "best antivirus", "best antispyware" or "antivirus comparison" "antispyware comparison"; there are some good reviews and tests regarding the topic. Here are some examples:
http://lifehacker.com/395046/five-be...s-applications,
http://www.av-comparatives.org/.
Some criteria on which you can base your decision are: infections detection rate or accuracy (based on tests performed by some companies and groups), system resources 'hunger' (how much resources it needs to run and if it is intrusive or not), type of license (commercial, shareware, free, open), ease of use and configuration, customer service quality, etc.
Currently I'm using Avira Antivirus for virus protection and a combination of Spybot-Spyware Blaster for spyware protection, and they all have worked very good for me in the past few months.
Here is the security bundle I usually recommend for Windows users:
Firewall: Comodo Firewall Pro - it's free, regarded as one of the best software firewalls today, with quick learning curve and an easy GUI for beginner or advanced configuration.
Antivirus: Avira or AVG - both have free versions which are quite good, also widely recommended. I don't know about the latest AVG version, but Avira also includes an anti-rootkit scan option.
Antispyware: Spybot which is a powerful and free application for spyware prevention and removal. You can accompany it with Spyware Blaster which is basically a spyware prevention tool.
If you are almost paranoid about your security, then you can also get Keyscrambler (an anti-keylogger) and JonDo (a proxy anonymization software to prevent spies from getting your real IP address).
I hope it helps, greetings.